A storage tank does something that no pump can do: it separates the rate at which water comes out of the ground from the rate at which you use it. That single change solves a large proportion of borehole problems.
Most boreholes cannot meet peak demand instantaneously. A borehole with a modest sustainable yield can still deliver a substantial volume over a full day - but ask it for that volume in twenty minutes and it will draw down to the pump intake and trip. A tank collects the water steadily and releases it quickly, which is exactly the wrong way round for a borehole and exactly the right way round for the property.
Borehole not keeping up with irrigation? Storage usually solves it better than a bigger pump.
Get a Tank Installation QuoteWhy Storage Is Usually Better Than a Bigger Pump
When a borehole struggles to keep up, the instinctive response is to fit a larger pump. This is almost always the wrong move, because the constraint is the borehole rather than the pump. A larger pump simply reaches the sustainable limit faster and then runs the level down.
Storage attacks the actual problem:
| Fitting a larger pump | Adding storage |
|---|---|
| Draws the borehole harder than it can sustain | Lets the borehole fill the tank at its own comfortable rate |
| Water level falls to the pump intake, risking dry running | Abstraction spread over hours, so drawdown stays modest |
| Frequent starts and stops, hard on the motor | Long, infrequent pump cycles, which suit a submersible motor |
| No buffer if the pump or power fails | Stored water available during outages and faults |
| Peak demand still limited by borehole yield | Peak demand met from storage, independent of instantaneous yield |
| Accelerates wear on the borehole and pump | Reduces stress on both |
The one situation where a larger pump is the right answer is where yield testing shows the borehole genuinely can sustain more and the existing pump is undersized for it. That is a question the test data answers.
How a Borehole-to-Tank System Works
The arrangement is straightforward, and its simplicity is part of the appeal:
- 1The submersible pump lifts water from the borehole to the tank at a rate within the borehole's sustainable yield.
- 2A float or level control stops the borehole pump when the tank is full and restarts it when the level drops to a set point.
- 3The tank holds the buffer volume, and any primary treatment is usually placed before the tank so stored water is already treated.
- 4A booster pump or pressure system draws from the tank and supplies the property at the pressure and flow required.
- 5A pressure vessel smooths delivery and limits how often the booster pump starts.
- 6An overflow handles the case where a level control fails, discharging safely rather than into a wall or foundation.
Where the tank can be elevated sufficiently, gravity can replace the booster pump for low-pressure applications such as drip irrigation - though the height required for useful pressure is more than most properties can practically achieve.
Sizing the Tank
Tank sizing balances the daily volume the borehole can produce against how the property uses water, plus whatever buffer you want for outages:
- Daily demand - the realistic total volume used across a day, including irrigation, which usually dominates
- Peak demand - how much is drawn at once, and for how long. Irrigation zones running simultaneously are the usual peak
- Sustainable borehole yield and the recommended daily running hours, from the test report
- Desired buffer - how many days of supply you want available if the pump fails or power is out
- Space and access - tank footprint, height, and whether it can physically be delivered to the position
- Aesthetics and planning - visual impact, screening, and any body corporate or estate requirements
The common mistake is sizing the tank against the borehole alone rather than against the pattern of use. A tank large enough to hold a day's production is not necessarily large enough to cover an irrigation peak plus a reserve. It is generally worth going somewhat larger than the minimum calculation, because the incremental cost of extra capacity is modest compared with the cost of the rest of the system.
Want backup water as well as buffer capacity? Size the tank for both while you are installing it.
Request a Storage QuoteTank Types and Siting
| Consideration | What to think about |
|---|---|
| Material | Polyethylene tanks are the common choice for domestic and light commercial use - durable, available in many sizes and straightforward to install. Larger installations may use sectional or steel tanks. |
| UV protection | Tanks are exposed to strong sunlight. UV-stabilised material and an opaque tank matter, because light promotes algae growth inside. |
| Colour and light | Darker, opaque tanks limit light penetration and therefore algae. A translucent tank in full sun will grow algae. |
| Position | Close enough to the borehole to keep pipe runs short, close enough to the point of use to limit friction losses, and accessible for cleaning and maintenance. |
| Base | A full, level, properly prepared base supporting the entire footprint. Water is heavy, and a tank on an inadequate or uneven base will deform and can fail. |
| Stands | Elevated stands must be engineered for the loaded weight. This is not a place for improvisation - a full tank on a failing stand is dangerous. |
| Multiple tanks | Often easier to site and deliver than one large tank, and linking them gives redundancy for cleaning. They must be properly interconnected to fill and draw evenly. |
| Inlet and outlet | Inlet above the maximum water level to prevent backflow, outlet positioned above the tank floor so settled sediment is not drawn into the system. |
Controls
The control arrangement determines whether the system runs itself or needs watching:
- Float valve or float switch to stop the borehole pump when the tank is full - the essential control on any tank system
- Low-level cut-out to stop the booster pump before it runs the tank dry, which protects the booster
- Dry-run protection on the borehole pump, independent of the tank level control
- Pressure switch and vessel on the booster side, with the vessel pre-charge set correctly
- Overflow routed to drain safely away from foundations, walls and paving
- Level indication so you can see what you have available without climbing up to look
- Municipal top-up where the tank also serves as backup storage - which must be arranged with proper backflow protection and an air gap, never a direct connection
Backflow protection is not optional. Where a tank is fed from both a borehole and a municipal connection, the two must be separated so that borehole water can never enter the municipal supply. This means a physical air gap at the tank inlet rather than a valve or a non-return device. It is a requirement, and it needs to be designed in rather than added later.
Storage as Backup Water
Many Cape Town properties install tanks for reasons that go beyond making the borehole work better. Stored water covers municipal interruptions, planned maintenance shutdowns and pressure problems, and it does so regardless of whether the borehole is running.
If backup is part of the reason for the tank, it changes the design: size the tank for the reserve you want in addition to the operational buffer, keep the reserve volume turning over rather than standing indefinitely, arrange the municipal top-up with proper air-gap separation, and think about how water is drawn if power is out. A booster pump on a tank is no use in an outage unless it has an alternative supply.
Keeping Stored Water in Good Condition
- Keep tanks opaque and lids sealed - light and open lids are what produce algae and insect problems
- Fit and maintain insect screening on vents and overflows
- Inspect internally and clean periodically, since sediment settles over time
- Draw from above the tank floor so settled material stays put rather than being pulled into the system
- Ensure the stored volume turns over rather than standing for long periods
- Where water is used domestically, include the tank in periodic water quality testing - a clean borehole can still deliver into a contaminated tank
What Affects Tank Installation Cost
- Tank capacity and how many tanks are installed
- Base preparation, and whether an engineered stand is required
- Distance from borehole to tank, and from tank to point of use - trenching and pipe runs
- Whether a booster pump and pressure vessel are included
- Control specification, from a simple float valve to full level control with indication
- Whether filtration is installed at the same time and where it sits
- Municipal top-up arrangement with backflow protection, where included
- Site access, particularly whether a large tank can physically be delivered to the position
Related Borehole Services
How much storage you need follows directly from what the borehole sustainably yields, which is set by the geology and the way the hole was constructed. Borehole Drilling Cape Town covers what determines yield and why it cannot be predicted before drilling.
Water Tank and Storage System Costs
Extra tank capacity is one of the cheapest things you can buy in a borehole system relative to everything around it, which is why it is usually worth going a size up rather than sizing to the minimum calculation.
| Item | Indicative range | What moves it |
|---|---|---|
| 2,500 L tank | R2,500 – R4,500 | Brand and whether it is UV-stabilised and opaque. Insist on both. |
| 5,000 L tank | R4,000 – R8,000 | The common domestic size. |
| 10,000 L tank | R12,000 – R25,000 | Delivery access becomes a real constraint at this size. |
| Level base preparation | R1,500 – R8,000 | A full, level base under the whole footprint. Water is heavy and an uneven base deforms a tank. |
| Engineered elevated stand | R8,000 – R40,000+ | Must be engineered for the loaded weight. Not a place to improvise. |
| Booster pump and pressure vessel | R5,000 – R18,000 | Flow and pressure required at the outlets. |
| Float and level control | R800 – R5,000 | Simple float valve versus full level control with indication. |
| Municipal top-up with air-gap separation | R1,500 – R6,000 | Required where the tank is fed from both sources. An air gap, not a valve. |
These are indicative ranges, not a quotation. They are compiled from published South African supplier and contractor pricing to give you a starting point for budgeting. They are not our rate card, and no figure here is a commitment.
Treat them as a broad guide only. Published borehole pricing in South Africa varies enormously - different 2026 guides quote per-metre drilling rates for the same province that differ by a factor of three - because depth, geology, access, specification, distance and fuel costs all move the number. Depth in particular is not known until the hole is finished. Figures generally exclude VAT unless noted, and change over time. Only an itemised written quote against your actual site means anything.
Borehole Tank Installation FAQs
Do I need a tank with my borehole?
It depends on the relationship between your borehole's sustainable yield and your peak demand. If the borehole comfortably meets peak flow, a direct pressure system is simpler and cheaper. If peak demand exceeds what the borehole can deliver at that moment - common where irrigation is involved - storage is usually the better answer.
A tank also gives you buffer during a power outage or pump fault, and it lets the borehole pump run in longer, less frequent cycles, which is easier on the motor.
What size water tank do I need for my borehole?
Size it against how you use water rather than against the borehole alone. Work from your realistic daily demand, your peak draw and how long it lasts, the borehole's sustainable yield and recommended running hours, and how much reserve you want for outages.
Irrigation usually dominates the calculation. It is generally worth going somewhat larger than the minimum figure, because extra capacity is inexpensive relative to the rest of the system and it gives you more operating margin.
Can borehole water and municipal water share a tank?
They can, and it is a common arrangement for backup storage, but the connection has to be made correctly. The municipal top-up must enter through a physical air gap above the maximum water level, so there is no possible path for borehole water to enter the municipal supply.
A valve or non-return device is not an acceptable substitute for an air gap here. This needs to be designed into the installation rather than improvised later.
Does the tank need to be raised for pressure?
Not usually, because the height needed for useful pressure is more than most properties can practically achieve - you need a great deal of elevation to generate meaningful pressure by gravity alone.
Most installations use a ground-level tank with a booster pump and pressure vessel, which gives consistent pressure regardless of tank level. Elevation can work for low-pressure applications like drip irrigation, but any stand must be engineered for the weight of a full tank.
How do I stop algae growing in my water tank?
Algae needs light, so the answer is to exclude it. Use an opaque, UV-stabilised tank in a dark colour rather than a translucent one, keep the lid properly sealed, and fit insect screening on vents and overflows.
Water that turns over regularly is less prone to problems than water standing for long periods. Periodic internal inspection and cleaning deals with the sediment that settles regardless.
Will a tank improve my water pressure?
The tank itself does not create pressure, but the system built around it does. A booster pump drawing from the tank with a properly set pressure vessel delivers consistent pressure that is independent of what the borehole is doing at that moment.
That often feels like a substantial improvement compared with a direct system where pressure sags as the borehole draws down. The gain comes from the booster and the buffer, not from the tank in isolation.
Can I use the tank as backup if the municipal supply is cut?
Yes, and that is a common reason for installing one. If backup is part of the purpose, size the tank for the reserve you want in addition to the operational buffer, and arrange any municipal top-up with proper air-gap separation.
Also think about power. A booster pump on a tank will not run during an outage unless it has an alternative supply, so consider how you would draw water if both the municipal supply and the power were off.
Where should the tank be positioned?
Close enough to the borehole to keep the pipe run short, close enough to the point of use to limit friction losses, on ground that can take the weight, and somewhere you can actually access it for cleaning and maintenance.
Delivery access matters too - a large tank has to physically reach the position. Where access is restricted, several smaller linked tanks are often easier than one large one, and they give you redundancy when one needs cleaning.
MAKE A MODEST YIELD GO FURTHER.
Storage lets a borehole meet peaks it could never supply on demand.
Get a Tank Installation QuoteGet a Borehole Tank Installation Quote
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